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    <title>Document</title>
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    <script>
        // 作用域链：函数使用变量的时候，采用最近原则。

        // 案例1：结果是几？
        var num = 456;
        function f1(){
            var num = 123;
            function f2() {
                var num = 0;
                console.log(num); //站在目标出发，一层一层的往外查找
            }
            f2();//0
        }
        f1();//0

        // 案例2：结果是几？
        var a = 1;

        function fn1(){
            var a= 2;
            var b = 33;
            fn2();

            function fn2(){
                var a =3;
                fn3();

                function fn3() {
                    var a =4;
                    console.log(a); //a的值？4
                    console.log(b); //b的值? 33
                }
            }
        }
    </script>
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